Conversion of an at-grade intersection into a diamond interchange is an expensive effort that in some instances could result in a multiple million-dollar project. However, there is very little information relating to the resulting safety improvements of this conversion relative to the original design.
Crash modification factors (CMFs) can be found in a clearinghouse which is a repository of CMFs from studies all over the world. This clearinghouse includes CMFs from one study in 2007 for the conversion to a diamond interchange based on a meta-analysis of evaluations from Europe. It is unknown how reliable and useful these specific CMFs if they were applied in the United States (U.S.). Therefore, there is a need to develop CMFs specifically for U.S. intersections.
The objective of this research is to develop a CMF for converting from an at-grade intersection to a diamond interchange. This evaluation will compile data from intersections that have been converted to diamond interchanges in multiple States in the U.S. Data will also be collected from reference sites (e.g., at-grade intersections) to allow for a reliable before-after evaluation that will yield a CMF with a high star rating in the CMF Clearinghouse to ensure the highest quality and confidence in the results of this study.